stephens



Feb. 18, 1964 D. R. STEPHENS 3,121,465

DEVICE FOR TREATING on. WELLS Filed Dec. 19, 1960 2 Sheets-Sheet 1 INVENTOR DONALD R. STEPHENS BY A a/ ki ATTORNEY Feb. 18, 1964 s P s 3,121,465

DEVICE FOR TREATING OIL WELLS Filed Dec. 19, 1960 2 Sheets-Sheet 2 IINVENTOR DONALD R. STEPHENS BY W-n/fini ATTORNEY United States Patent I 3,121,465 DEVECE FOR TREATING OiL WELLS Donald R. Stephens, Martinsburg, W. Va., assignor to E. I. du Pont de Nemonrs and Compan wiiniington, Del., a corporation of Delaware Filed Dec. 19, 1960, Ser. No. 76,803 1 Claim. (GI. 166164) The present invention relates to a device for stimulating fluid flow from a low permeability oil or gas well. More particularly, this invention is concerned with a device for injecting a reactive liquid into perforations in the surrounding strata to purge the perforation and to increase the flow area of the perforation.

Perforating of the well casing and the surrounding strata is not always suificient to produce a flow area suitable for eflicient production from the bearing strata. For instance, conventional perforating methods frequently leave carbonaceous, hydrocarbonaceous, and siliceous deposits inside the perforations which at least partially clog the perforations. Additionally, during the perforating of the well casing and surrounding strata, the walls of the perforation may be compacted into an almost impermeable zone.

For efiicient production of the well, the clogging deposits must be removed, the compacted zone about the perforation must be loosened, and the porosity of the walls must be increased. Treatment of the perforated area by suitable chemicals may remove the undesirable materials and increase the porosity of the perforation walls. The chemicals which are the most effective for treating the perforations, however, are usually very corrosive toward the well casing. Furthermore, no means are available for injecting the chemical into the perforations at sufficient pressure to enhance the purging action.

These difficulties are overcome in accordance with this invention by an apparatus comprising a dual-walled cylindrical carrier, the innermost Walls of which define a central chamber, the annulus between said dual-walls defining an annular chamber; a structural member holding said carrier rigidly in place and sealing the top and bottom thereof; and a pressure-generating means located within the central chamber, the annular chamber containing a liquid reactive with undesirable material in the well perforations. The side walls of the carrier comprise a resilient material rupturable at a predetermined pressure provided by the pressure-generating means. More specifically, the dual-Walled cylindrical carrier comprises a first cylindrical body, the innermost walls of which define a central chamber and a second cylindrical body of greater diameter than the first cylindrical body, concentric with and spaced from the first cylindrical body to form an annular chamber. A fixed structural member is fitted at the top and bottom of the cylindrical bodies to seal the ends and hold the bodies rigidly in place.

The pressure-generating means preferably comprises a non-detonating propellant charge located within the central chamber. Any propellant charge which provides the proper pressure-time relation for functioning of the device may be used. Suitable non-detonating propellant charges include defiagrating or low explosives such as black powder or smokeless powder.

The amount of propellant used will vary according to the length of the apparatus, the pressure in the well, the

viscosity of the reactive liquid and other variables. In

general, the amount of propellant should be sufiicient to develop a pressure of at least 150 pounds per square inch above the well pressure within the assembly.

The propellant charge may be initiated by any conventional initiation means, preferably an electrical igniter. Another preferred pressure-generating means comprises 3,121,465 Patented Feb. 18, 1964 arranging a liquid, a piston and a propellant charge successivcly in the central chamber. A particularly preferred embodiment utilizing this means comprises a first cylindrical body having perforated side walls, the innermost side wall of which defines a central chamber; a second cylindrical body of greater diameter than the first cylindrical body concentric with and fitting over the first body thereby closing oft" the perforated side wall; a third cylindrical body of greater diameter than the second cylindrical body concentric with and-spaced from the second cylindrical body to form an annular chamber, said chamber containing a reactive liquid; a structural member fixed at one end of the three cylindrical bodies to seal said bodies and hold them rigidly in place; a second structural member fixed at the other end of the three cylindrical bodies to seal said bodies and hold them rigidly in place, the second structural member having an inner chamber which mates with the central chamber defined by the first cylindrical body to form a lengthwise chamber; a liquid material, a piston and a propellant charge arranged successively from bottom to top, respectively, in the length-wise chamber; and initiating means in contact with the propellant charge. The side walls of at least the second and third cylindrical bodies comprise a resilient material which is rupturable at the pressure generated by the liquid material being forced through the perforated side wall of the first cylindrical body by the piston upon initiation of the propellant charge.

In each of the preferred embodiments, pressure is generated in the central chamber. This pressure expands the walls of the outer cylindrical body against the perforated well casing or well walls. As the pressure further increases, the outer walls of the cylindrical body rupture at the areas in contact with the perforations and the reactive liquid is expelled at high pressure directly into the perforations where it performs a purging and cracking action.

Preferred embodiments of the present invention are described in the accompanying drawings wherein:

FIG. 1 is a section through a well showing one embodiment of the invention in place in the perforated section of the well casing;

FIGURE 2 is an enlarged detailed section taken of the device at a portion of the carrier Wall adjacent a perforation in the casing after the wall has been ruptured; and

FIGURE 3 is a section through a well showing another embodiment of the invention in place in a perforated section of well casing.

In FIGURE 1, the numeral 1 designates structural end members, e.g., of steel, connected by axial member 2. Cylindrical bodies 3 and 4 are sealed to the two end members by a suitable bond. A propellant charge 5 is contained in the central chamber formed by the innermost wall of cylindrical body 4. In the annular chamber formed by the annulus between the inner cylindrical body 4 and outer cylindrical body 3 is contained a reactive liquid 6. An igniter 7 is positioned in the propellant chamber with suitable electrical connections to a conventional firing head attached to the wire-line cable 8. Both cylindrical bodies 3 and 4 comprise an expandable material which is resistant to corrosion by the liquid 6 under conditions prevailing in the well and which will rupture at the pressure generated by initiation of propellant charge 5.

In practice, the igniter is electrically fired which in turn initiates the propellant charge. Pressure is generated in the propellant chamber 5 causing the outer cylindrical body 3 to expand against the well casing 9. As the pressure in the propellant chamber continues to increase, the outer cylindrical body 3 ruptures in the 3 areas where the casing has been perforated, as shown in FIGURE 2. As the pressure in the propellant chamber continues to increase the inner cylindrical body 4 expands, forcing the reactive liquid directly into the perforations 10. During the generation of pressure, the length of the device remains constant since the two end pieces are rigidly fixed and sealed by axial member 2 and end members 1. After the liquid has been injected into the perforations, the device is retrieved from the borehole.

Due to the pressures developed while forcing the reactive liquid into the perforation using the device of the present invention, cracks may be developed in the strata surrounding the perforation. If desired, propping agents, such as sand, may be added to the reactive liquid to insure that the fractures remain open.

In FIGURE 3, the numerals 11 and 1 designate structural end members, e.g., of steel, connected by a first cylindrical body 12 which contains perforations 13. Outer cylindrical body 14 and inner cylindrical body 15 are formed of an expandable material which is resistant to attack by the liquid 16 under conditions prevailing in the well and which will rupture at a predetermined pressure. These cylindrical bodies are sealed to the end members 11 and 1.1 by a suitable bond. The central chamber 23 defined by the innermost walls of cylindrical body 12 and the chamber 17 defined by the upper structural end member 11 mate to form a lengthwise chamber. A liquid 16 is contained in this lengthwise chamber. Above the liquid is piston 18 which is actuated by a propellant charge 19 ignitable by a conventional igniter 20. In the annulus between cylindrical bodies 14 and 15 is contained a liquid 22 reactive with undesirable material in the perforations 21. The device is suspended in the casing by a firing head attached to a cable 8.

In operation, the ignition of the propellant by the igniter forces the piston down against the fluid in the lengthwise chamber, causing the liquid to be forced out through the perforations 13 against the inner cylindrical body 15. The force exerted causes the outer cylindrical body 14 to expand against the casing wall and further exertion of pressure causes the cylindrical bodies to break at the areas in contact with perforations in the casing. Thus the reactive liquid 22 is expelled directly into the perforations in the casing and the surrounding strata. Since the end members are held in place and do not expand, the force of the expansion is concentrated on the side walls. The device remains as one unit; and, after the liquid has been expelled, the device may be retrieved from the casing.

Specific embodiments of the present invention are described in the following examples.

Example 1 A dual-walled cylindrical unit is prepared as illustrated IN FIGURE 1. The bottom end piece is 4- /8 inches in diameter and is formed of a globular shaped piece of structural-grade steel cut so that its thickness graduates from 1.5 inches at its outer edge to 3 inches at its center. A 3 foot long column of 1.5-inch O.D. steel is welded to the center portion of the end piece. Two 38 inch long tubes of A; inch thick nautral rubber having diameters of 2 inches and 4 inches, respectively, are secured to the end piece by means of a mechanical clamp so that they extend upward concentrically of the center steel column and are held upright by a brace while being filled. The annulus between the steel column and the innermost rubber tube is filled with 3182 grams of smokeless powder (density, 1.0), and the annulus between the two rubber walls is filled with 5090 grams of a 70% aqueous solution of perchloric acid (density, 1.6). A conventional electric squib is positioned adjacent the uppermost portion of the mass of smokeless powder. Then an end piece of 1.5 inch-thick disc structural-grade steel having an outer diameter of 4% inches and a central hollowed out section threaded to mate with a conventional firing head is placed on the filled unit, so that the lead wires of the squib are in contact with the firing mechanism in the head, and the rubber tubes are secured to this steel disc by a mechanical clamp.

The unit thus assembled is lowered into an oil well containing drilling mud until it is in contact with the previously perforated section of the casing. The smokeless powder is deflagrated by means of the electric squib. The pressure built up by the deflagration of the smokeless powder is calculated to be 44,000 pounds per square inch. This pressure is sufficient to inject the reactive liquid into the perforations in the formation where it cleans the hole. The cleansing effect of the reactive liquid is evident by the improved flow from the perforated section of the oil well after the dual-walled unit is removed.

Example 2 An assembly is constructed resembling that described in FIGURE 3. In this assembly the lower structural end member is 4% inches in diameter and is graduated in thickness from 1.5 inches at its outer edges to 3 inches at the central globular section. This member is welded to a 3 foot length of perforated pipe which has an outer diameter of 2 inches and an inner diameter of 1.32 inches. The perforations in this pipe are inch in diameter on 2 inch centers and are staggered at intervals about the pipe. Two concentric 38 inch long tubes of /s-inchthick polyethylene, wherein the outermost tube has an outer diameter of 4 inches and the inner tube has a diameter of 2 /8 inches, are secured at one end to the lower end piece by a conventional mechanical clamp. The annulus formed between the tube walls is filled with 3941 grams of a 50% solution of hydrofluoric acid (density, 1.15). The upper portions of these polyethylene tubes are secured by a mechanical clamp to an upper end piece of steel which is 4% inches in diameter and which extends 25 inches above the upper portion of the axial supporting member. This upper end piece is hollowed out to form an inner chamber which is threaded to mate with the axial supporting member at its lower portion and with a conventional firing head at its upper section. The diameter of the lower (neck) portion of this chamber is 1.32 inches and the height of this neck portion is 2 inches. The central chamber is filled with 3500 grams of water.

' Above the water a piston head comprising a three inch O.D. disc of one inch thick steel is positioned. The space above the piston head is filled with 2600 grams of slowburning smokeless powder (density, 1.0), and an electric squib is inserted into the mass of powder. The firing head then is screwed to the upper portion of the end member so that the lead wires from the squib are in contact with the electrical wires in the head. The assembly then is lowered into an oil well casing which is filled with drilling mud and which has been perforated pre viously by means of a conventional perforating gun. When the assembly is adjacent a perforation section of this borehole, the smokeless powder is deflagrated by the electric sqiub. After the charge has been deflagrated the assembly is removed from the casing. Performance of the well indicates that the perforations are free of deposits which would impede production of the well.

The device of the present invention may be used in porous open holes when the surrounding strata is of a noncrumbling nature, as well as previously perforated casings.

Suitable reactive liquids for use in treating and fracturing the strata include hydrofluoric acid, perchloric acid, dilute hydrochloric acid, sulfuric acid and various other acids and conventional fracturing agents which will react with the material in the borehole to form easily removable products. If a strong oxidizing agent is used, carbon residues present in the perforation are eliminated.

Any liquid, reactive or not, may be used in the lengthwise chamber of the embodiment of FIGURE 3.

Suitable resilient materials for use as the side walls relatively high melting polymers, e.g. films of polyethylene, polypropylene, polystyrene, polyvinylidene chloride, or polytetrafluoroethylene, and the lil: The resilient material should be inert to the reactive fluid used in treating the strata at oil well temperatures and should possess structural strength sumcient to resist deformation at the temperature and pressures encountered in the oil well casing. The thickness of the resilient material used preferably will vary from .012 inch to 0.250 inch. At thicknesses below 0.012 inch the structural strength of the side walls would not be sufiicient to withstand the pressure exerted in the oil well casing at the depth of the perforations. If a resilient material having a thickness greater than 0.250 inch is used, the thickness of the side walls will prohibit maximum loading of the propellant charge and the reactive liquid. Naturally, the thickness of the material used for the side walls will depend upon the physical characteristics of the resilient material. For example, a m airetalhvafilZhETAOCMFWSHRDLUSHR ample, a material having a relatively high shear strength would be used relatively thin sections whereas a material having a relatively low shear strength could be used in comparatively thicker sections. If desired, the side walls may be formed so that the thickness of the resilient material near the metal end pieces is greater than its thickness in the areas which are intended to rupture.

The device of the present invention is advantageous since it may be easily lowered into the open holes or casing using conventional wire line tools. Since the rupturing of the outside wall occurs only at the areas already perforated, there is no diluting or spraying of the liquid used to purge the perforations, consequently the cleaning and fracturing action is more effective. Obviously, many additions and modifications may be made without departing from the scope of the invention.

I claim:

A device for injecting a reactive liquid into well perforations comprising a first cylindrical body having perforated side walls, the innermost side wall of which defines a central chamber; a second cylindrical body of greater diameter than said first cylindrical body concentrio with and fitting over the first cylindrical body thereby closing off the perforated side wall; a third cylindrical body of greater diameter than said second cylindrical body concentric with and spaced from said second cylindrical body to form an annular chamber, said chamber containin a reactive liquid; a so'uctural member fixed at one end of the three cylindrical bodies to seal said bodies and hold them rigidly in place; a second structural member fixed at the other end of the three cylindrical bodies to seal said bodies and hold them rigidly in place, said second member having an inner chamber, said inner chamber mating with said central chamber defined by the first cylindrical body having perforated side walls to form a lengthwise inner chamber; a liquid material, a piston and a propellant charge arranged successively from bottom to top, respectively in said lengthwise inner chamber; said piston being initially positioned above said perforations and being adapted to provide, upon actuation, compressive force to propel said liquid through said perforations, and initiating means in contact with said propellant charge; the side walls of said second and third cylindrical bodies comprising a resilient materal which is rupturable at the pressure generated by the liquid material as it is forced .through the perforated side walls of said first cylindrical body by the piston upon initiation of the propellant charge.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,356 Pitzer Feb. 13, 1940 2,233,930 Witt Mar. 4, 1941 2,740,478 Greene Apr. 3, 1956 

